1. Field of the Invention
The present invention relates generally to a hand tool, and more particularly to an electric power tool capable of switching various operation modes by a single switch.
2. Description of the Related Art
Typically, a conventional electric power tool includes a motor, a planetary gear reduction mechanism, an impact mechanism, and a hammer mechanism. A shaft of the motor is connected to the planetary gear reduction mechanism to change the speed thereof, and the impact mechanism is connected to the planetary gear reduction mechanism. The conventional impact mechanism includes a shaft and an impact member. The shaft is driven by the planetary gear reduction mechanism. The shaft has slots thereon, in which balls are received. The impact member is fitted to the shaft through the balls. The impact member has two blocks on a top thereof. A spindle, which is connected to the shaft of the impact mechanism, has two arms interacted with the blocks of the impact member. In a normal condition, the shaft will drive the impact member and the spindle rotation together. Under a condition of a resistance on the spindle, the impact member will be reciprocated by the interaction of the blocks of the impact member and the arms of the spindle that the impact member will generate an impact effect, and we call it as “impact mode”. In the conventional electric power tool, a stopper is provided behind the impact member to stop the impact member moving backwards that no impact effect when the stopper behind the impact member. The stopper may be moved away to give a sufficient space behind the impact member that the impact member may provide impact effect. The detail structure and function of the impact mechanism are taught by U.S. Pat. No. 7,308,948.
Typically, the hammer mechanism is provided in front of the impact mechanism, which includes a first teeth disk and a second teeth disk, and the first teeth disk is fixed and the second teeth disk is free to rotate. The second teeth disk is connected to the spindle and rotated together with the spindle. A cam is provided behind the first teeth disk to move the first teeth disk to engage or disengage the second teeth disk. The hammer mechanism will generate a vibration effect when the teeth disks are engaged together. We call it as “hammer mode”. The detail structure and function of the hammer mechanism is taught by U.S. Pat. No. 6,142,242.
When both of the impact mechanism and the hammer mechanism are shut, the spindle is rotating in a maximum power, and we call it as “drill mode”. Recently, the electric power toll provides “driver mode”. In “driver mode”, the power is adjustable.
In the electric power toll of early time, there are two independent switches on the toll to control the impact mechanism and the hammer mechanism respectively. It is inconvenient to consumers. In recent time, however, there are electric power tool equipped with single switch to control all operation modes, for example U.S. Pat. No. 7,308,948. Because the stopper, which is the main device to switch “impact mode”, and the cam, which is the main device to switch “hammer mode” are far away from each other that the switch to control both modes usually has a complex structure.